Texas Instruments CD74HC4538E

Overview

CD74HC4538E from Texas Instruments is a dual retriggerable/resettable monostable multivibrator in 16-pin PDIP package, operating from 2V to 6V with ±25mA output drive, Schmitt-trigger inputs on A/B, and independent trigger/reset propagation delays unaffected by external timing components RX/CX. It delivers precise pulse widths (e.g., 0.63–0.81 ms with RX=10kΩ, CX=0.1µF) for timing-critical control logic in industrial sequencers and test equipment.

For engineers reviewing the CD74HC4538E datasheet, CD74HC4538E pinout, CD74HC4538E application, or CD74HC4538E equivalent, key selection criteria include its retriggerable edge-triggering capability (A leading / B trailing), buffered Q/Q outputs, wide -55°C to +125°C temperature range, and compatibility with both LSTTL and CMOS input logic levels.

Technical Context

The CD74HC4538E implements two independent monostable circuits, each with separate A (leading-edge), B (trailing-edge), R (reset), RX, and CX terminals. Its internal architecture uses Schmitt-trigger inputs for noise immunity and latched flip-flop stages to ensure stable output transitions independent of RX/CX values.

Propagation delay (tPLH/tPHL) ranges from 43 ns to 375 ns depending on VCC and load, while retrigger time (trT) is fixed at ≤175 ns at 5V - both parameters remain invariant across RX and CX component variations, enabling predictable timing in variable-precision applications.

Key Specifications

Pinout & Package

CD74HC4538E is housed in a 16-pin plastic dual in-line package (PDIP-N), 0.300" wide, with standard through-hole mounting and 0.1" pin pitch. Pin 1 is marked by a notch or dot; pin 8 is GND and pin 16 is VCC.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual monostable multivibrator applications.

Compared with CD74HC4538M and CD74HCT4538E, the CD74HC4538E offers broader voltage flexibility (2V–6V), through-hole ease-of-use, and identical timing performance - making it ideal for development, industrial control, and multi-rail systems where layout adaptability and supply headroom matter.

Availability

CD74HC4538E is available at Aetrix Electronics and suitable for industrial sequencers, automated test equipment, power supply monitors, and digital communication interfaces requiring stable component supply across extended temperature ranges.

Supply support for CD74HC4538E includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader delivering analog, embedded processing, and logic solutions with emphasis on reliability, longevity, and industrial-grade qualification.

The CD74HC4538E belongs to TI's High-Speed CMOS Logic family, designed specifically for precision timing applications demanding retriggerable behavior, wide temperature operation, and robust noise immunity in harsh environments.

FAQ

What is the minimum external timing resistor value supported by the CD74HC4538E?

The CD74HC4538E specifies a minimum external timing resistor RX of 5 kΩ. Using lower values risks exceeding the 30 mA maximum current into pins 2 or 14, potentially causing timing inaccuracy or device stress. This limit ensures reliable operation across the full -55°C to +125°C temperature range and maintains pulse width predictability per τ ≈ 0.7 × RX × CX.

Can the CD74HC4538E operate reliably at 3.3V supply voltage?

Yes, the CD74HC4538E operates fully specified from 2V to 6V, including 3.3V. At VCC = 3.3V, it maintains Schmitt-trigger input thresholds (~1.0V VIH min, ~0.33V VIL max), 43–375 ns propagation delays, and ±25mA output drive - making it suitable for direct interface with 3.3V microcontrollers and FPGAs without level translation.

How does the retriggerable mode differ from non-retriggerable mode in the CD74HC4538E?

In retriggerable mode, each new trigger pulse (on A or B) extends the output pulse width by one full τ period - ideal for extending timeouts during ongoing activity. In non-retriggerable mode (achieved by connecting Q to B for A-triggering or Q to A for B-triggering), only the first trigger initiates the pulse; subsequent triggers are ignored until completion - useful for fixed-duration gating independent of input frequency.

What is the purpose of the RXCX pins (pins 1, 2, 14, 15) on the CD74HC4538E?

The RXCX pins on the CD74HC4538E connect external timing components: RX (resistor) between VCC and RXCX, and CX (capacitor) between RXCX and GND. These define the monostable pulse width τ ≈ 0.7 × RX × CX for each section. Pins 1/14 serve MONO1; pins 2/15 serve MONO2 - enabling independent timing control for dual-channel applications like dual-phase delay generation.

Does the CD74HC4538E require external pull-up or pull-down resistors on unused inputs?

Yes. Unused A inputs must be tied to GND; unused B inputs must be tied to VCC. This prevents floating inputs from inducing erratic triggering due to noise or leakage. Unused reset inputs should also be pulled high (to VCC) to avoid unintended device reset. These terminations ensure deterministic startup and stable operation per TI's functional specifications.